What is herein referred to as lift-regulating means relates to any type of active aerodynamic control surfaces which are adapted to alter the surface of the wind turbine blade so as to regulate the lift thereof. In particular, such lift-regulating means allow load alleviation, and/or higher lift at a start-up procedure of the turbine. For blades with lift-regulating means, flow sensing is an important topic, see e.g. T. K. Barlas and G. A. M. van Kuik. “State of the art and prospectives of smart rotor control for wind turbines”, The Science of Making Torque from Wind; Journal of Physics: Conference Series, volume 75, 2007. This is regardless of the particular embodiment of the lift-regulating means, for example whether it is embodied as rigid hinged flaps, (see e.g. WO2009056136), or pneumatic flexible trailing edges without hinges, (see e.g. WO2008132235, or WO2007045940).
To obtain the flow data, in particular angle of attack, and load data, it has been suggested to use pitot tubes and/or pressure tabs, see e.g. H. A. Madsen and A. Fischer, “Wind shear and turbulence characteristics from inflow measurements on the rotating blade of a wind turbine rotor” 2009, presented at 2009 European Wind Energy Conference and Exhibition, Marseille (FR), 16-19 Mar. 2009. Disadvantages of such sensors are mainly their high extra costs, as well as reliability and servicing issues, which are a hindrance to using them in serial production.
Another idea to sense local loading, disclosed in WO2009056136, is to directly measure the hinge moment acting upon an installed trailing edge flap. This input can then be utilised to control the flap movement directly. No sensor parts outside the blade are needed, and one can think of a variety of very robust hinge moment sensors. However, where such trailing edge flap hinge moment is measured, there is a desire to further improve the control of the lift-regulating means.